EN
There were no differences in body weight and height at withers at 360 days of age and in daily gains from 121 to 360 days between Lowland Black- White and Lowland Red-White bulls. Sires of these two breeds with daily body gains exceeding 1300 g produced semen with higher spermatoa concentration and motility. Lowland Black-White bulls with high growth rate produced less semen during two years, their ejaculates had lower volume when compared to their counterparts. Quite opposite results were obtained in high growth rate Lowland Red-White group of bulls. Correlations between body weight at 360 days as well as daily gains and semen traits were weak and often negative within group of Lowland Black-White bulls but within Lowland Red-White bulls all these correlations were stronger and positive. It was concluded that body growth rate of bulls during rearing had no large and negative effect on their subsequent semen production during the first two years of performance in A.I. stations.